Originally Posted by barth2k
I am trying to picture how edge lit local dimming works and I can't.
You can't picture it because it doesn't work
even though Samsung often markets it like it does. (Note: It could absolutely work if there were LEDs around all 4 edges of the display. As far as I know, few (no?) current LCD TVs are made this way, instead they use LEDs along two edges.)
What Samsung can
do is divide the screen into a series of horizontal rectangles (how many, I don't know) that are then dimmed individually. Now, keep in mind there are LEDs on each vertical edge of the TV, so light from the left edge is mostly asked only to get to the middle; same with light from the right edge. The light guides are designed in such a way that you don't see a seam in the middle, so there is some overlap, but it does let you double the number of zones.
The maximum possible number of zones is, therefore, (number of LEDs in each edge-lighting "bar" x 2). Practically, there are almost certainly fewer than that for a couple of reasons. (1) Rectangular zones of this type (half the width of the screen, horizontally) don't often align with content in a perfect manner. How many shots are there of an often coffin, for example? (2) You can't overly dim one zone next to another zone with any local dimming, but it'd be especially harsh with these very rectangular geometric zones.
Except for special cases when you can dim an entire horizontal band of pixels, like the black bars on wide scope movies.
Let's take the simple case where you want to black out 4:3 side bars. It's not like you can tell the light "go dark ~1/4 way across the screen then light up, then go dark again when you reach ~3/4 of the way.". That's voodoo physics. Unless you have top and bottom as well as side LEDs. But that's a lot of trouble to go through just to black out side bars. And it still does not help you If you want to display, say, a white circle in the center against black background.
So edgelit local dimming seems like an oxymoron to me.
More or less.